This invention relates to a method for preparing a single layer carbon nano-tube.
In recent years, a minute cylindrical fiber having a single cylindrical structure of not more than 3 nm outer diameter made of carbon, especially graphite, so-called carbon nano-tube has been noted. Such the carbon nano-tube has been conventionally prepared in such a manner as described below.
That is to say, in convention, DC arc discharge is generated between a pure carbon electrode as a cathode and a metal-added carbon electrode as an anode in an atmosphere of rare gas or mixed gas of rare gas with hydrocarbon. Then, evaporation of the electrode takes place at the anode. That is to say, the metal and the carbon evaporate at the same time from the anode. The evaporated carbon appears as soot in which a single layer nano-tube having nearly uniform outerdiameter is, eventually, contained, since the evaporated metal acts to the evaporated carbon as a catalyst.
It has been conventionally known that the preparation efficiency of the single layer carbon nano-tube increases extremely by adding two kinds of metal catalysts into the anode in the aforesaid method for preparing the single layer carbon nano-tube.
In the prior method for preparing the single layer nano-tube, a good deal of carbon evaporated from the electrode is build up on the cathode as deposits without becoming soot containing the single layer carbon nano-tube because of using DC arc discharge. There is, therefore, a problem that the yield of the single layer carbon nano-tube is small. Further, in the prior method, since the evaporation of carbon takes place at one electrode and does not take place at the other electrode, there is also a problem that the yield of soot containing the single layer carbon nano-tube is small.
And, the deposits build up on the cathode has electrical resistance different from that of materials of cathode, and further is not only apt to be distorted in its shape because of not being build up in the central portion of the cathode, but also brittle. And there is, therefore, a problem that discharge becomes unstable because of growth or omission of the deposits.
Furthermore, in the prior method, when plural metal catalysts are used, all the metal catalysts must be added to the anode, and, therefore, there is a problem that a preparation of the diode is difficult.